In modern surgery, powered surgical tools are some of the most-important instruments medical personnel have available for performing certain surgical procedures. Many surgical tools take the form of a motorized handpiece to which a cutting accessory, like a drill bit, a bur or a saw blade, is attached. These tools selectively remove sections of hard or soft tissue or separate tissue. The ability to use powered surgical tools on a patient has lessened the physical strain of surgeons and other personnel when performing surgical procedures on a patient. Moreover, most surgical procedures can be performed more quickly and more accurately with powered surgical tools than with the manual equivalents that preceded them.
Some surgical handpieces include pneumatically driven motors. Internal to this type of handpiece is a motor that comprises a housing in which a set of vanes are located. The vanes are attached to a rotating shaft that extends out of the housing. The shaft is connected to the cutting accessory. Compressed gas is introduced into the housing. The flow of the compressed gas causes the vanes and shaft to rotate. The rotation of the shaft, in turn, causes the cutting accessory to move. Depending on the type of gear assembly used to couple the cutting accessory to the shaft, the accessory may rotate in a unidirectional pattern, oscillate around an axis, reciprocate back and forth along a longitudinal axis or oscillate back and forth along a sagital plane. The exact motion that the cutting accessory undergoes is a function, of the design of the handpiece and the gear assembly used to transfer the rotational moment of the shaft to the cutting accessory.
An advantage of a pneumatically driven surgical handpiece is that, when it is operated for an extended period of time, the temperature of the handpiece does not appreciably rise.
The efficient operation of a pneumatically driven surgical handpiece is facilitated by the inclusion of aerosol of oil in the pressurized gas supplied to the motor. The oil lubricates the interface between the vanes and the adjacent inner surface of the motor housing. The oil both reduces wear on the vanes and minimizes the noise generated as a consequence of the vanes moving against the housing.
A number of assemblies are available to supply the oil aerosol to the compressed gas stream supplied to a surgical tool. However, some of the assemblies require a significant amount of disassembly in order to refill their oil reservoirs. Still other assemblies require manual setting before surgery. A limitation associated with some assemblies is that they do not supply adequate quantities of oil to the handpiece motors when the motors are initially cycled on. Consequently, for a short period of time when the handpiece is first actuated, it runs “dry”. As a result, when the handpiece is initially actuated, until the vanes are properly lubricated, the vanes are subjected to significant wear and the motor generates an appreciable amount of noise.
There have been efforts at providing oilers that operate based on the Venturi principal. This type of oiler has an opening exposed to the gas flow to the handpiece motor. The flow of the pressurized gas induces the flow of oil out of the oiler. Some of these assemblies are constructed to have wicks in their openings. The wicks regulate, dampen, the flow of oil out of the oilers. A disadvantage of these oilers is that they tend to supply excess oil during the initial period in which their complementary motors are actuated. It is further observed the wicked versions of these oilers tend to not deliver sufficient oil at the end stage of the use cycle.
During a surgical procedure, a handpiece is cycled on and off a number of times. Owing to the repetitive on and off operation, the number of times during a surgical procedure the handpiece is run dry, the wear to which the vanes can be exposed can be significant.
Also, as mentioned above, the cycling of the motor on and off with an in-line oiler often results in the delivery of excess oil during the initial stage of the use cycle. The introduction of this unneeded oil into the motor can reduce the performance of the motor. Moreover, the excess oil has a tendency to leak from the tool assembly. Clearly, this is something that should be avoided in a surgical environment. Moreover, this excess discharge can occur each time the motor is cycled on. Collectively, these excess discharges can cause the unnecessary and undesirable exhaustion of the oil supply. When this occurs, the surgical procedure may even need to be interrupted in order to refill or replace the oiler.